Focus distance from a DSLR lens to the subject

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Focus distance from a DSLR lens to the subject

Postby chaos133 on Sun May 29, 2011 5:32 pm

Hey, I was wondering how you find out the focus distance from a DSLR lens to the subject? For example on Pocket Digital Camera Specs it will say something like 1cm focus (so the lens can focus on a subject as long as it's 1cm or more away. I can't seem to find this information on DSLR lens specs. I'm not looking at a particular lens I just want to know what to look for in the specs to find out this information.

Thanks for anyones help :)
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Re: Focus distance from a DSLR lens to the subject

Postby the foto fanatic on Sun May 29, 2011 6:14 pm

Hi and welcome

It is usually able to be found on the manufacturer's specs. I just had a quick peek at the Nikon Aus web pages and they have it as "Closest Focusing Distance"

If you are looking at specs on a retailers' site you might be better off going to he lens makers' site.
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Re: Focus distance from a DSLR lens to the subject

Postby Matt. K on Sun May 29, 2011 6:19 pm

And the million dollar question is.....does this distance change as you change F/stops?????? Or does only the depth of field change? :D :D :D :D :D :D :D :D
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Re: Focus distance from a DSLR lens to the subject

Postby surenj on Sun May 29, 2011 7:10 pm

Chaos, the minimum focusing distance is generally LENS specific. Just look in the lens info.
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Re: Focus distance from a DSLR lens to the subject

Postby chaos133 on Sun May 29, 2011 9:02 pm

Matt. K wrote:And the million dollar question is.....does this distance change as you change F/stops?????? Or does only the depth of field change? :D :D :D :D :D :D :D :D


I thought only the depth of field would change when I change the F/stops, and it doesnt effect the minimum focusing distance. Am I correct?

Thanks for the help everyone :)
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Re: Focus distance from a DSLR lens to the subject

Postby Wink on Sun May 29, 2011 9:33 pm

Do you have an iPhone?
There's an app called iDof Calc which will calculate focus distance with min and max points for any focal length at any subject distance. It also takes crop factor into account.
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Re: Focus distance from a DSLR lens to the subject

Postby Mr Darcy on Sun May 29, 2011 11:40 pm

chaos133 wrote:
Matt. K wrote:And the million dollar question is.....does this distance change as you change F/stops?????? Or does only the depth of field change? :D :D :D :D :D :D :D :D


I thought only the depth of field would change when I change the F/stops, and it doesnt effect the minimum focusing distance. Am I correct?

Thanks for the help everyone :)

The minimum focus distance is the minimum distance that the lens is absolutely sharp. and will not change. It has to do with physics. As you decrease aperture, the acceptable depth of field will increase. This may bring the effective focus closer to the lens than the minimum focus distance.
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Re: Focus distance from a DSLR lens to the subject

Postby aim54x on Mon May 30, 2011 12:04 am

Mr Darcy wrote:The minimum focus distance is the minimum distance that the lens is absolutely sharp. and will not change. It has to do with physics. As you decrease aperture, the acceptable depth of field will increase. This may bring the effective focus closer to the lens than the minimum focus distance.


But with most Macro lenses that distance is TINY!! :cheers:
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Re: Focus distance from a DSLR lens to the subject

Postby ATJ on Mon May 30, 2011 10:16 am

Wink wrote:Do you have an iPhone?
There's an app called iDof Calc which will calculate focus distance with min and max points for any focal length at any subject distance. It also takes crop factor into account.

Unless the app has an exhaustive list of lenses, it will not at all answer the OP's question. Minimum focus distance is dependent on the lens construction and in particular how far out the lens element can be screwed. It is very specific to each make/model of lens.

Further, I suspect that it is also of little value for macro work because a) many macro lenses change their focal length when they get to macro focusing distances and b) depth of field in macro work is dependent on magnification and not focal length.
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Re: Focus distance from a DSLR lens to the subject

Postby ATJ on Mon May 30, 2011 10:44 am

the foto fanatic wrote:It is usually able to be found on the manufacturer's specs. I just had a quick peek at the Nikon Aus web pages and they have it as "Closest Focusing Distance"

Note that for Nikon, the closest focusing distance is generally the distance from the camera's focal plane (where the sensor or film are) rather then the distance from the front of the lens. I don't believe any manufacturers list the latter.

For example, my Nikkor 60mm f/2.8D has a closest focusing distance listed as 219mm but at this point the front of the lens is around 70mm from the subject.
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Re: Focus distance from a DSLR lens to the subject

Postby Murray Foote on Mon May 30, 2011 3:54 pm

Another factor is that sharpness is relative. Take any photographic image and blow it up enough and the image will break down. What we see as sharp is partly the physical properties of our eyes and partly psychological - the way our brain interprets the image data our eyes feed it. Also, there is no point at which a lens suddenly becomes sharp where it wasn't at all before, it's a gradation. Depth of field tables often include both critical and liberal boundaries of focus. Moreover, if you have a poor quality lens it may appear to have a poorer zone of focus than a high quality lens.

This means that if you really want to find out the boundaries of sharpness for a lens and camera, you should start from the manufacturer's specifications and then shoot test images under various conditions and apertures to see what you think is sharp. What is sharp will also depend on how you present the image - for web or for print, small or large, and viewing distance for a print. It will also depend on your camera technique, whether you use a tripod, mirror lockup etc and whether you sensitively and effectively sharpen in post-processing.

So ask the question by all means and you may get a useful answer, but there's often really no substitute for working things out by yourself to your own satisfaction.
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